Ch 7 Glycolysis Respiration and Fermentation2

Glycolysis, Respiration, and Fermentation

Overview of Cellular Respiration

• Cellular Respiration: A set of metabolic (redox) reactions

  • Equation: Glucose + 6 Oxygen → 6 Carbon Dioxide + 6 Water + Energy (ATP)

  • Reactants: Glucose and Oxygen

  • Products: Carbon Dioxide, Water, ATP

  • Process: Stepwise breakdown of high energy glucose to low energy CO2

  • Type of Reaction: Exergonic (energy is released)

  • Energy Production: ADP + P → ATP

  • Location: Mitochondria of the cell

  • Requirement: Oxygen (Aerobic process)

Mitochondria

• Structure:

  • Double membrane organelles, known as the 'Power House of the cell'

  • Outer Membrane: Smooth and permeable

  • Inner Membrane: Highly convoluted into folds (Cristae)

  • Matrix: Semifluid, filled with enzymes for sugar breakdown

  • Contains the Electron Transport Chain (ETC)

Stages of Cellular Respiration

• Four Stages:

  1. Glycolysis: Captures energy as ATP and NADH

  2. Prep Reaction: Captures energy as NADH

  3. Citric Acid Cycle: Captures energy as ATP and NADH

  4. Oxidative Phosphorylation: Uses NADH to produce a large amount of ATP

Glycolysis

• Definition: Literally means "sugar splitting"

• Function: First step in glucose metabolism

• Location: Cytoplasm of the cell

• Oxygen Requirement: Anaerobic (doesn't require oxygen)

• Process:

  • Breaks one glucose molecule into two pyruvate molecules

  • Reaction: Glucose (C6) → 2 Pyruvate (C3) + 2 ATP

Phases of Glycolysis

• Energy Investment Phase:

  • Uses 2 ATP to split glucose into two smaller sugars

  • Reactants: 1 Glucose, 2 ATP

  • Products: 2 G3P

• Energy Harvesting Phase:

  • Reactants: 2 G3P, NAD+

  • Products: 2 Pyruvate, 2 NADH, 4 ATP

  • Net Gain: 2 ATP (4 ATP formed - 2 ATP used)

NAD+ Requirement

• Critical Component:

  • Glycolysis requires NAD+

  • Without sufficient NAD+, glycolysis cannot continue, leading to cell death

Relationship to Photosynthesis

• Shared Components:

  • G3P: Intermediate of glycolysis, also produced in the Calvin cycle

  • NADH/NADPH: Products of glycolysis and photosynthesis

  • ATP: Produced in glycolysis and used in photosynthesis

Cellular Respiration Stages

Stage 2: Prep Reaction

• Function: Links glycolysis to the citric acid cycle

• Location: Mitochondrial matrix

• Oxygen Requirement: Aerobic (requires oxygen)

• Reaction:

  • Pyruvate (C3) → Acetyl CoA (C2) + CO2

  • Reactants: Pyruvate, CoA, NAD+

  • Products: Acetyl CoA, CO2, NADH

  • Each glucose yields 2 Acetyl CoA

Stage 3: Citric Acid Cycle

• Also Known As: Krebs cycle

• Location: Mitochondrial matrix

• Oxygen Requirement: Aerobic

• Reaction:

  • Acetyl CoA (C2) → 2 CO2 + ATP

  • Reactants: Acetyl CoA, NAD+, FAD, ADP

  • Products: CO2, ATP, NADH, FADH2

  • Produces: 4 CO2, 2 ATP, 6 NADH, 2 FADH2 per glucose

Stage 4: Oxidative Phosphorylation

• Function: Major ATP production occurs here

• Process:

  • NADH and FADH2 donate electrons to the Electron Transport Chain

  • Location: Cristae of the mitochondria

  • Oxygen Requirement: Aerobic

  • Reactants: NADH, FADH2, Oxygen

  • Products: ATP, Water, NAD+, FAD

Phase I: Electron Transport Chain

• Process:

  • Creates a Hydrogen ion gradient using energy from electrons

  • Electrons are accepted by oxygen, forming water

Phase II: Chemiosmosis

• Process:

  • H+ flows down the gradient through ATP Synthase, driving ATP synthesis

  • ATP produced: 1 NADH = 3 ATP; 1 FADH2 = 2 ATP

Fermentation

• Purpose: Regenerate NAD+ in absence of oxygen

• Process:

  • Converts Pyruvate into Organic acids/Alcohol + CO2

  • Generates a net of 2 ATP

• Types:

  • Lactic Acid Fermentation: Produces lactate (in animals)

  • Alcoholic Fermentation: Produces ethanol and CO2 (in plants)

Summary

• Glycolysis breaks down glucose into two pyruvate molecules with a net gain of 2 ATP.

• The citric acid cycle removes high-energy electrons used by the electron transport chain to generate ATP.

• In the absence of oxygen, fermentation ensures the regeneration of NAD+, enabling glycolysis to continue.